NOTE 6. PROPERTY AND EQUIPMENT

The following is a summary of the categories of our property and equipment:

Depreciation expense was approximately $12.0 million and $12.4 million for the years ended December 31, 2018 and 2017. Included in this amount is $53,000 and $93,000 for the years ended December 31, 2018 and 2017 on assets acquired under capital lease obligations. Accumulated depreciation associated with these capital lease obligations was $0.1 million and $0.8 million at December 31, 2018 and 2017.

We periodically review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be fully recoverable. Our review requires us to estimate the fair value of assets when events or circumstances indicate that they may be impaired. The fair value measurements for our long-lived assets use significant observable inputs that reflect our own assumptions about the estimates that market participants would use in measuring fair value including assumptions about risk. If actual future results are less favorable than the assumptions and estimates we used, we are subject to future impairment charges, the amount of which may be material. There were no indications of impairment during the year ended December 31, 2018.